1. Field of the Invention
The present invention relates generally to an intravascular implant and methods of using the implant within the vasculature of the body, particularly adjacent to vascular aneurysms. The present invention also relates to the attachment of a second implant, such as a vascular graft, to the intravascular implant.
2. Description of the Related Art
An aneurysm is an abnormal dilatation of a biological vessel. Aneurysms can alter flow through the affected vessel and often decrease the strength of the vessel wall, thereby increasing the vessel's risk of rupturing at the point of dilation or weakening. Implanting a vascular prosthesis through the vessel with the aneurysm is a common aneurysm therapy. Vascular grafts and stent grafts (e.g., ANEURX® Stent Graft System from Medtronic AVE, Inc., Santa Rosa, Calif.) are examples of vascular prostheses used to treat aneurysms by reconstructing the damaged vessel.
Stent grafts rely on a secure attachment to the proximal, or upstream, neck of an aneurysm, particularly for aortic abdominal aneurysms (AAA), but several factors can interfere with this attachment. The proximal neck of the aneurysm can be diseased. This diseased tissue can by a calcified and/or irregularly shaped tissue surface for which the graft must to attach. Healthy, easily-attachable tissue is often a distance away from the aneurysm. For example, in AAAs the nearest healthy vascular tissue may be above the renal arteries. Even a healthy vessel can be so irregularly shaped or tortuous that a graft may have difficulty attaching and staying sealed. Furthermore, the proximal neck can shift locations and geomtries over time, particularly over the course of aneurysm treatment and reformation of the aneurysmal sack. This shifting and shape changing of the vessel can result in partial or total dislodgement of the proximal end of a currently available stent graft.
Devices have been developed that attempt to solve the issue of vascular graft attachment. International Publication No. WO 00/69367 by Strecker discloses an aneurysm stent. The stent has a securing mechanism that attaches to the vascular wall proximal to the renal arteries, which is typically where healthier vascular tissue is located when a patient has an AAA. The stent also has a membrane that is placed at the proximal end of a stent graft and forms a seal in the vessel. Strecker, however, discloses a securing mechanism with ball-ended struts which angle away from the seal. The ball-ends will reduce the pressure applied by the struts onto the vascular wall, and the struts are angled improperly to insure the best anchor. If the graft begins to dislodge into the aneurysm, the struts will tend to fold inward and slide with the graft instead of engaging frictionally into the vascular walls to prevent dislodgement.
U.S. Pat. No. 6,152,956 to Pierce discloses a radially expandable collar connected by connecting wires to an expandable stent. The stent also has barbs with sharp ends that spring radially outward to embed into the walls of the vascular tissue. The stent, however, is expandable, but once expanded cannot be easily contracted. The stent, therefore, can not be repositioned if incorrectly placed during initial deployment. Further, the barbs do not angle toward the seal and will not engage into the vascular wall for additional anchoring force, should the prosthesis begin to become dislodged.
U.S. Pat. No. 6,361,556 by Chuter discloses a stent for attaching to grafts, where the stent is connected to an attachment system for anchoring to the vessel. The attaching system has hooks angled toward the graft. The attachment system has no way of being repositioned during deployment. Further, the stent is a substantially rigid, balloon expandable stent and therefore maintains a fixed diameter and resists deformation from forces imposed by the vascular environment. The stent, therefore, can not be easily repositioned during deployment and may not seal the graft under changing geometric conditions over time.
There is thus a need for a device and method that can securely anchor a vascular graft within a vessel and can seal the graft regardless of the existence of diseased tissue at the sealing location. There is also a need for a device that can be deployed to the vasculature while minimizing bloodflow obstruction to the main vessel and to branching vessels. A need also exists for a device and method that can accomplish the above needs and adjust to tortuous vasculature. There is also a need for a device and method that can accomplish the above and have dimensions and a placement location that can be adjusted multiple times in vivo, even after the anchor has been fully deployed. There is also a need for a device that can be delivered through a low profile catheter. Additionally, there is a need for a device that can anchor into a different portion of tissue from which it seals, so as not to overstress any individual portion of vascular tissue or any elements of the implant, thus preventing fractures in the tissue and of the implant.